Field
The present disclosure relates to a touch sensitive element and a display device including the same. More particularly, the present disclosure relates to a touch sensitive element with improved modulus and vibration strength and a display device including the same.
Description of the Related Art
In response to users' demand, a touch type display device, which touches a display device to input information, has been developed and broadly used for various display devices including a liquid crystal display device and an organic light emitting display device. Therefore, research has continued to utilize a haptic device to provide direct and various tactile feedback to the users.
According to the related art, a vibration motor such as an eccentric rotating mass (ERM) or a linear resonant actuator (LRA) is used for the display device as a haptic device. The vibration motor is configured to vibrate the entire display device. However, the vibration motor is not suitable for a flexible display device because of various problems. One problem is that it is difficult to modulate the frequency to adjust the level of vibration because the size of a mass must be increased in order to increase the vibration strength. Another problem is that the response speed of the vibration motor is very slow.
In order to solve the above-described problems, a shape memory alloy (SMA) and electroactive ceramics (EAC) have been developed as materials for the haptic device. However, it is difficult to apply the shape memory alloy and the electroactive ceramics to the display device (e.g., a flexible display device) because the shape memory alloy (SMA) has a slow response speed, a short lifespan, and an opaque property. Also, the electroactive ceramics (EAC) are breakable.
Therefore, haptic devices using an electroactive polymer (EAP) have recently attracted attention. The electroactive polymer is a polymer which may be deformed by an electrical stimulation and may repeatedly expand, contract and bend due to an electrical stimulation. Among various types of electroactive polymers, a ferroelectric polymer and a dielectric elastomer are mainly used. For example, the ferroelectric polymer includes a poly vinylidene fluoride (PVDF), and the dielectric elastomer includes a silicon-based polymer, a urethane-based polymer, an acrylic-based polymer, and the like.
However, PVDF, which is representative of the ferroelectric polymer, has a relatively excellent modulus. However, the PVDF involves a polling process using a high voltage of 4 KV or higher. As such, PVDF is dangerous due to the process characteristics. The dielectric elastomer has an excellent light transmittance and an optical property, but the permittivity is relatively lower than the ferroelectric polymer. Therefore, it is difficult to use the dielectric elastomer for a display device whose voltage is relatively low, such as a mobile display, because the driving voltage of the dielectric elastomer is high.
Therefore, studies for an electroactive polymer which not only satisfies a process stability, a permittivity, and light transmittance characteristics, but also improves the modulus and the vibration strength of the haptic device are required.